linux-kernel - [PATCH 4/4] x86/percpu: Introduce %rip-relative addressing to PER_CPU

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Date:   Thu, 12 Oct 2023 18:10:39 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 4/4] x86/percpu: Introduce %rip-relative addressing to PER_CPU_VAR macro

Introduce x86_64 %rip-relative addressing to PER_CPU_VAR macro.
Instruction with %rip-relative address operand is one byte shorter than
its absolute address counterpart and is also compatible with position
independent executable (-fpie) build.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 arch/x86/include/asm/percpu.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 34734d730463..9a5f1896c5ef 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -4,16 +4,18 @@
 
 #ifdef CONFIG_X86_64
 #define __percpu_seg		gs
+#define __percpu_rel		(%rip)
 #else
 #define __percpu_seg		fs
+#define __percpu_rel
 #endif
 
 #ifdef __ASSEMBLY__
 
 #ifdef CONFIG_SMP
-#define PER_CPU_VAR(var)	%__percpu_seg:var
+#define PER_CPU_VAR(var)	%__percpu_seg:(var)##__percpu_rel
 #else /* ! SMP */
-#define PER_CPU_VAR(var)	var
+#define PER_CPU_VAR(var)	(var)##__percpu_rel
 #endif	/* SMP */
 
 #ifdef CONFIG_X86_64_SMP
-- 
2.41.0